docs: def evaluate(ctx, model, corpus, clusters):
      """Evaluate performance of POS Tagger."""
      click.echo('chemdataextractor.pos.evaluate')
      if corpus == 'wsj':
          evaluation = wsj_evaluation
          sents = list(evaluation.tagged_sents())
          for i, wsj_sent in enumerate(sents):
              sents[i] = [t for t in wsj_sent if not t[1] == '-NONE-']
      elif corpus == 'genia':
          evaluation = genia_evaluation
          sents = list(evaluation.tagged_sents())
          # Translate GENIA bracket tags
          for i, genia_sent in enumerate(sents):
              for j, (token, tag) in enumerate(genia_sent):
                  if tag == '(':
                      sents[i][j] = (token, '-LRB-')
                  elif tag == ')':
                      sents[i][j] = (token, '-RRB-')
      else:
          raise click.ClickException('Invalid corpus')
      tagger = ChemCrfPosTagger(model=model, clusters=clusters)
      accuracy = tagger.evaluate(sents)
      click.echo('%s on %s: %s' % (model, evaluation, accuracy))